As everyone knows, LED illumination has irreplaceable advantages, such as energy saving, low power consumption, and electrical-to-optical conversion efficiency near to 100%. It can save more than 80% energy compared with the traditional light source with the same illuminating efficiency and has a longer service life. In view of the above advantages, the LED is more and more used as a light source such as a lot of LED retrofit lamps in the market. Such LED retrofit lamps have the same appearance and profile as the traditional light source such as incandescent lamp or lamp tube, thus they can be more applicable to the existing illuminating systems as a light source.
An LED retrofit lamp is disclosed in the prior art. The LED retrofit lamp has a lamp holder connected with a power supply a heat sink that has one end fixed on the lamp holder and the other end thermally contacting a printed circuit board carrying an LED chip, and a hemispherical bulb provided at the other end of the heat sink to enclose the printed circuit board carrying the LED chip. The heat sink of such LED retrofit lamp is configured to be hollow with an LED driver arranged therein for the LED chip. However, the light intensity distribution of such LED retrofit lamp is not quite uniform because the bulb used as a diffuser usually has a simple structure made from a glass or plastic, while such diffuser cannot distribute the light according to requirements and merely can slightly change the beam angle.
Another prominent shortcoming is a low inner space utilization ratio of such LED retrofit lamp. In the existing LED retrofit lamp, the LED chip usually should be arranged uniformly and symmetrically on the printed circuit board in order to distribute the light on various directions as uniformly as possible. In this situation, the printed circuit board divides the LED retrofit lamp into two parts, i.e. a heat sink part below the printed circuit board, and a bulb part over the printed circuit board. As the LED driver for driving the LED chip is arranged in the heat sink, and the inner space of the heat sink is limited, the volume of the LED driver is required to be reduced as small as possible. As everyone knows, reduction of the volume of the electronic device leads to notable increase of the cost, which obviously increases the cost of the LED retrofit lamp.